Cavity microwave filter design is a well established art and practical designs exist, in particular, for combline and interdigital filters. Such filters, however, often are fabricated of several separately fabricated elements (e.g. cavity walls, resonators, frequency and coupling trimming devices and end resonator taps) which then have to be assembled to exacting tolerances to achieve the desired filter transmission parameters. Such fabrication and assembly is costly in terms of labor man hours. Efforts, therefore, have been made to reduce the fabrication cost. For example, U.S. Pat. No. 4,791,717 discloses a construction method, for an interdigital filter integrated into a down converter, which attempts to reduce the number of separate parts to be assembled by bending a specially cut piece of sheet metal to form part of a cavity housing.
Other U.S. Patents of interest are U.S. Pat. Nos. 2,530,691, 3,737,816, 3,925,883, 4,647,882, 4,802,234, 4,837,535, 4,849,724, 4,963,844 and 4,970,480.